Relatively-dense carbon/carbon composites have been found to be highly useful in a variety of structural applications. Because of certain characteristics, such as high strength, high stiffness, light weight, high temperature resistance, and advantageous frictional properties, these composites are desirably suited for use, for example, in the aerospace and automotive brake pad industries. They are favored for use in high-end automotive transmissions but high costs have prevented widespread utilization.
Dense carbon/carbon composite structures typically include a carbon fiber matrix, wherein the interstices in the fiber matrix are at least partially filled with deposited carbon. The carbon fibers are high in strength, and are typically in the form of a woven or non-woven fabric or mat. In either case, the carbon fibers provide the composite with structural reinforcement.
To fill the carbon fabric with additional carbon, the fibers are typically placed in a chamber, where they are heated and exposed to a carbon-based vapor. Carbon from the vapor is thereby deposited on the heated fabric via chemical vapor deposition.
In an alternative method for depositing carbon, the fiber fabric is placed in a chamber filled with liquid precursor (cyclohexane, for example), and the fibers are heated to pyrolize the liquid precursor at the surface of the fabric. The pyrolysis of the precursor produces a vapor that deposits carbon on the fibers within the fabric. This process is referred to as “rapid densification” and is described in greater detail in U.S. Pat. No. 5,389,152, issued to Thurston et al.
Though the above-described methods are known to produce high-quality composite structures, the commercial application of these structures is limited by the high cost of carbon fibers, processing and energy consumption. Accordingly, the application of these methods to mass-production industries, such as automobile manufacturing, has thus far been greatly limited due to economic feasibility. Further, due to the axially-elongated structure of the fibers, the composite properties are generally non-isotropic and highly dependent on fiber orientation.